Today, tableware washed by machine often has to meet more stringent requirements than tableware washed by hand. Thus, even dishes completely freed from food remains are evaluated as unsatisfactory when, after machine dishwashing, they still show whitish stains which are attributable to water hardness or other mineral salts and which emanate from dried-on water droplets through lack of wetting agents.
Accordingly, in order to obtain sparkling tableware without any stains, rinse agents are now being successfully used. The addition of rinse agents at the end of the wash program ensures that the water drains completely from the tableware so that, at the end of the wash program, the various surfaces are free from residues and sparkling.
Commercially available rinse agents are mixtures of nonionic surfactants, solubilizers (for example cumenesulfonate), organic acids (for example citric acid) and solvents (for example ethanol), water and optionally preservatives and perfumes. The function of the surfactants in these rinse agents is to influence the interfacial tension of the water in such a way that it drains from the tableware in a thin coherent film so that no water droplets, streaks or films remain behind after the subsequent drying phase (so-called wetting effect). Another function of the surfactants is to suppress the foam caused by food residues in the dishwashing machine. Since the rinse agents generally contain acids to improve the clear drying effect, the surfactants used also have to be relatively stable to hydrolysis by acids.
In addition, only biodegradable, toxicologically and dermatologically safe ingredients are now considered for use in rinse agent formulations. Accordingly, the surfactants used in the rinse agents also have to exhibit these properties.
EP-B1 0 197 434 (Henkel) describes rinse agents which contain mixed ethers as nonionic surfactants. Many different materials (glass, metal, silver, plastic, china) are cleaned in dishwashing machines. This range of materials has to be thoroughly wetted in the final rinse cycle. Rinse agent formulations containing mixed ethers as sole surfactant component meet these requirements to only a limited extent, if at all, so that the clear rinse or drying effect is unsatisfactory, particularly on plastic surfaces.
DE-A1 19 611 999 and WO 94/13618 describe alkoxylated carboxylic acid esters which are obtained by homogeneous catalysis in the presence of hydroxides and reducing agents or a co-catalyst. According to both these documents, such compounds may be used in laundry detergents, dishwashing detergents and cleaners.
DE-A-43 26 112 describes low-foaming multipurpose cleaners which contain alkoxylated carboxylic acid esters in admixture with alkyl glycosides and optionally other surfactants, such as alkyl sulfates, alkyl ether sulfates and fatty alcohol polyglycol ethers. These multipurpose cleaners are intended for cleaning hard surfaces, such as clinker bricks, ceramic tiles, enamels, PVC or wooden floors. In contrast to rinse agents, however, multipurpose cleaners always contain anionic surfactants. In addition, multipurpose cleaners, unlike rinse agents, are intended to generate a rich initial foam. Finally, other surfactant concentrations are used in multipurpose cleaners. Accordingly, multipurpose cleaners and rinse agents have to meet different requirements.
The problem addressed by the present invention was to provide new ecologically and toxicologically safe rinse agents which would be at least equivalent to commercially available rinse agents in their performance properties and which would not have any of the disadvantages mentioned above.